In ionographic devices such as that described by US-A 4,524,371 to Sheridon et al. or US-A 4,463,363 to Gundlach et al., an ion producing device generates ions to be directed past a plurality of modulation electrodes to an imaging surface in imagewise configuration. In one class of ionographic devices, ions are produced at a coronode supported within an ion chamber, and a moving fluid stream entrains and carries ions produced at the coronode out of the chamber. At the chamber exit, a plurality of control electrodes or nibs are modulated with a control voltage to selectively control passage of ions through the chamber exit. Ions directed through the chamber exit are deposited on a charge retentive surface in imagewise configuration through control of the modulation electrodes to form an electrostatic latent image developable by electrostatographic techniques for subsequent transfer to a final substrate. The arrangement produces a high resolution non-contact printing system.
Corona efficiency in ionographic heads is very low, on the order of 0.1% to 0.5%, when efficiency is defined as the ratio of the current reaching the electroreceptor to the total current within the corona chamber. Space charge, which builds up within the ion chamber and the modulation channel, serves to quench the corona. This can be overcome by increasing air flow velocity through the head. One limitation on this method of improving corona efficiency is the increasing machine noise accompanying increased air flow. Dirt management and the high cost of the larger capacity air flow device are other problems. However, the air entrainment has been seen as required to provide a satisfactory source of corona current, and as a side benefit, assists in removing corona effluents and byproducts that tend to cause long term damage to the print head. Even with air entrainment of ions, images formed still have a low contrast or development voltage, which causes problems with the eventual development of the image. While a printhead requiring no additional air flow apparatus would be desirable, the problems recited are required to be overcome.
US-A 4,725,731 to Lang, shows, in a scoroton for xerographic processes where a substantial, uniform charge is to be deposited on a surface preparatory to imagewise discharge, that a pin array coronode, preferably comprising saw tooth member with an array of projections forming the teeth thereof, produces a relatively uniform, high corona current. It is also known that pin array coronodes produce a significant amount of highly directed corona wind. Corona wind refers to the occurrence of ionized air molecules acquiring a significant velocity, such that the momentum of the molecules carries them towards the surface to be charged.
Pin array coronode corotron and scorotron devices are well known, as shown for example in US-A 4,725,731 to Lang and 4,591,173 to Gundlach. Pin array coronodes are also known for use in certain ionographic-type printing devices, such as for example, US-A 3,623,123 to Jvirblis, which shows the use of a pin array in association with a controllable grid network for printing characters. US-A 3,765,027 to Bresnick shows the use of a single pin to print in association with a character mask. 4,357,618 to Ragland shows pins or stylii apparently contacting a charge retentive surface for image formation. By way of background, US-A 4,697,196 to Inaba et al., 4,408,214 to Fotland et al., 4,558,334 to Fotland, US-A 4,658,275 to Fujii et al. and Canada 743,646 to Fauble, all show ion printing devices with various ion generation arrangements. US-A 4,584,592 to Tuan et al. demonstrates a modulation arrangement for imagewise modulation. These references are specifically incorporated herein by reference.